Exhaust gas treatment devices are used on automobiles to reduce atmospheric pollution from engine emissions. Examples of widely used exhaust gas treatment devices include catalytic converters and diesel particulate traps.
A catalytic converter for treating exhaust gases of an automotive engine includes a housing, a fragile catalyst support structure for holding the catalyst that is used to effect the oxidation of carbon monoxide and hydrocarbons and the reduction of oxides of nitrogen, and a mounting mat disposed between the outer surface of the fragile catalyst support structure and the inner surface of the housing to resiliently hold the fragile catalyst support structure within the housing.
A diesel particulate trap for controlling pollution generated by diesel engines generally includes a housing, a fragile particulate filter or trap for collecting particulate from the diesel engine emissions, and a mounting mat that is disposed between the outer surface of the filter or trap and the inner surface of the housing to resiliently hold the fragile filter or trap structure within the housing.
The fragile catalyst support structure generally comprises a monolithic structure manufactured from a frangible material of metal or a brittle, ceramic material such as aluminum oxide, silicon dioxide, magnesium oxide, zirconia, cordierite, silicon carbide and the like. These materials provide a skeleton type of structure with a plurality of gas flow channels. These monolithic structures can be so fragile that even small shock loads or stresses are often sufficient to crack or crush them. In order to protect the fragile structure from thermal and mechanical shock and other stresses noted above, as well as to provide thermal insulation and a gas seal, a mounting mat is positioned within the gap between the fragile structure and the housing.
Exhaust gas treatment devices typically comprise an end cone region between the fragile catalyst support structure or fragile particulate filter or trap and the exhaust pipe. According to certain embodiments, the end cone for an exhaust gas treatment device comprises an outer metallic cone; an inner metallic cone; and cone insulation disposed between said outer and inner metallic end cones. The end cone for an exhaust gas treatment device may comprise an outer metallic cone and a self-supporting cone insulation disposed adjacent the inner surface of said outer metallic end cone.
Mounting mats are often subject to local differences in gap bulk density and thermal gap expansion; that is, the gap bulk density and thermal gap expansion are not constant throughout the mounting mat. These local differences can contribute to undesirable support mat erosion upon exposure to hot exhaust gases.